The invention relates to a continuous casting mold for the continuous casting of a steel billet, preferably for the casting of thin slabs of a thickness of less than 100 mm, with wide side walls located opposite one another and with narrow side walls which are arranged clampably between the wide side walls and displaceably along the wide side walls transversely to the casting direction and are located opposite one another and which narrow in a wedge-shaped manner in the casting direction. The wide side walls have a funnel-shaped pouring-in region which extends in the casting direction as far as the mold end, and the distance between the wide side walls is reduced continuously, at least over part regions of their extent, in the direction of the narrow side walls and in the casting direction, and the wide side walls are designed to converge.
A continuous casting mold of the generic type is already known from DE-C 35 01 422. Its wide side walls are designed to converge in the direction of the narrow side walls and in the casting direction. The wide side walls have, in the region of adjustment of the narrow side walls, planar contact faces which cooperate with the side walls of the narrow side walls. When format adjustment is to be carried out in the mold, this usually involves a displacement of the narrow side walls with the effect of changing the width of the steel billet to be cast.
The billet thickness and consequently the distance between the wide side walls are in this case to be kept constant. However, during format adjustment of the known continuous casting mold, it is possible to keep the distance between the wide side walls constant only when the narrow side walls are offset both in the horizontal and in the vertical direction. Designing the wide side walls in the region of adjustment of the narrow side walls with a planar surface makes it necessary for the latter to be in a skew position with respect to the mold longitudinal axis. Due to these geometric restrictions, it is no longer possible for the exit cross section to be configured in such a way that, for each billet format to be cast, the billet thickness is constant over the entire billet width.
EP 0 658 387 A1 also discloses a continuous casting mold, the wide side walls of which are designed to converge in part regions in the direction of the narrow side walls and in the casting direction. The wide side walls have, in the region of adjustment of the narrow side walls, planar surface contours which cooperate with the side faces of the narrow side walls and the distance between which decreases linearly in the direction of the narrow side walls and is constant in the casting direction. In the event of a displacement of the narrow side walls with the effect of changing the wide sides of the steel billet to be cast, this embodiment also automatically necessitates an adjustment of the thickness of the latter in a ratio permanently predetermined by the geometry. However, the range of billet formats to be cast by means of a continuous casting mold of this type is consequently restricted in an undesirable way.
The object of the invention is, therefore, to avoid these disadvantages described above and to propose a continuous casting mold with a funnel-shaped pouring-in region, said mold allowing format adjustment in which the billet width of the billet to be cast can be set without any repercussion on the billet thickness and the billet thickness of the billet to be cast can be kept constant over the entire billet width.
This object is achieved, according to the invention, in that the distance between the wide side walls at the mold end is constant over the entire width of the wide side walls and at least one of the wide side walls is arranged on a mold carrying structure displaceably and tiltably with respect to the opposite wide side wall and is connected to an adjusting device. As compared with funnel molds in which the wide side walls are located opposite one another in a plane-parallel manner in the region of adjustment of the narrow side walls, the converging run of the wide side walls in the region of adjustment results in smaller curvatures in the funnel-shaped pouring-in region and consequently in the easy formation of a billet shell.
The proposed mold geometry, aimed particularly at the low-stress and therefore crack-free formation of a billet shell, gives rise, during format adjustment, to a wedge-shaped gap between the wide side wall and the narrow side wall, which, however, amounts at most to only a few millimeters and can easily be compensated by means of the tilting movement of the wide side wall. If one of the two wide side walls located opposite one another is firmly anchored on the mold carrying structure and thus forms a fixed side, the narrow side wall arranged between these two walls is also tilted by means of the displaceable and tiltable wide side wall and in this way a gap-free mold cavity for the reception of melt is formed for each adjustable billet format.
The tilting of the narrow side walls when they are clamped between the wide side walls is avoided and the necessary tilting angle for the wide side wall is halved when each of the wide side walls is arranged displaceably and tiltably on a mold carrying structure and is connected to an adjusting device.
In an expedient embodiment of the continuous casting mold, the wide side walls located opposite one another are connected to an adjusting device covering both wide side walls. In a special design solution, the tiltable wide side wall is connected to the adjusting device in an articulated manner.
Optimum conditions in the continuous casting mold are obtained for the formation of a billet shell when, with respect to a horizontal plane incorporating the casting level under constant casting conditions, the inclination xe2x88x9d1 of the wide side wall in the funnel-shaped pouring-in region is 1xc2x0 to 5xc2x0 and the inclination xe2x88x9d2 of the wide side wall in the region of adjustment of the narrow side wall is between 0.1xc2x0 and 0.3xc2x0.
In continuous casting technology, it is generally customary to clamp the narrow side walls between the wide side walls by means of a casting cone which is format-dependent, that is to say dependent on the casting width, the casting cone being adapted during format adjustment to the new billet format in each case. According to the teaching given in DE-C 35 01 422, it is advantageous for the narrow side walls to be arranged between the wide side walls in a position in which they diverge from one another in the casting direction. Both the mass flow of the steel in the direction of the narrow side walls and the cooling-related contraction of the billet may be taken into account in defining the casting cone.
A simple design of the continuous casting mold according to the invention is achieved in that each wide side wall is fastened releasably to a supporting wall and the adjusting device is connected to at least one of the supporting walls, which are displaceable and tiltable jointly with the wide side wall. The coolant ducts for mold cooling are worked into the wide side wall or the supporting wall in the form of coolant slots along the contact plane between the wide side wall and the supporting wall.
According to an alternative embodiment, a carrier wall is arranged between the wide side wall and the supporting wall, the wide side wall being fastened releasably to the carrier wall and the carrier wall being fastened releasably to the supporting wall. The coolant ducts for mold cooling are worked into the wide side wall or into the carrier wall in the form of coolant slots along the contact plane between the wide side wall and the carrier wall. By means of this embodiment, it is possible to preassemble the wide side wall jointly with the carrier wall and with the integrated coolant lines as a structural unit and to install it in the continuous casting mold in a simple way.
In order to meet the need for discharging the heat in the continuous casting mold differently in different zones, it is proposed, according to a preferred embodiment, that the geometry of the coolant ducts in the funnel-shaped pouring-in region of the wide side walls and the geometry of the coolant ducts in the region of adjustment of the narrow side walls be different. What is to be understood by the geometry of the coolant ducts is, on the one hand, the distance between the coolant ducts and, on the other hand, the clear width (cross-sectional area) of the coolant ducts and consequently the coolant flow velocity or the combination of the two influencing variables. The specific heat flux density of the wide side walls is varied as a result of both measures. According to a further possible embodiment, this is achieved in that groups of adjacent coolant ducts are conductively connected to individually activatable coolant stations, the funnel-shaped pouring-in region and the regions of adjustment of the narrow side walls of each wide side wall each being assigned at least one coolant supply station.
In order to allow an optimum discharge of heat in the continuous casting mold, it is advantageous for at least those inner walls of the wide side walls which form the mold cavity to be formed by different materials in the casting direction, the material used in the region of the casting level having a lower thermal conductivity than the material used for the portion of the wide side walls which follows in the casting direction. For example, in the region of the casting level, where particularly high temperatures occur and solidification is not required immediately, the wide side walls consist of nonferrous metals, refractory materials or various combinations of these.
It is particularly cost-effective and operationally reliable to equip the adjusting devices for the wide side walls and the narrow side walls with electromechanical or hydraulic drives.
Favorable conditions for the starting operation and for stress-free formation of a billet shell are likewise obtained when the contour of the wide side walls in the funnel-shaped pouring-in region is shaped parabolically in the casting direction. A further improvement in these conditions arises when the contour of the narrow side walls is also shaped parabolically in the casting direction and the narrow side walls are provided on both sides with edge clearances in a region which extends below the casting level as far as the mold exit.
Further advantages and features of the present invention may be gathered from the following description of unrestrictive exemplary embodiments, reference being made to the accompanying diagrammatic figures, which show the following: